One recent process consists in, first of all, carrying out in known manner the polymerization of a monomer, especially, olefin or diolefin in the presence of an anionic catalyst system comprising an organometallic compound of a metal of the Groups I, II or III of the Periodic Table and a compound of a transition metal; thereafter, without deactivating this catalyst system, the polymer which is obtained has added thereto a monomer which can be subjected to radical polymerization, and a radical catalyst, especially oxygeen or peroxide, and the polymerization of this second type is allowed to be effected. Such operations are described in U.S. Pat. No. 3,277,210 for the particular case of ethylene and vinyl acetate, while as regards other monomers, the operations are described in French Pat. No. 1,531,409 and the report of J.L. JEZL, N.S. CHU and E.M. KHELGHATIAN, entitled: "Anionic free radical polymers of alphaolefins" and presented during a congress held at San Francisco from the March 31 to the April 5th 1968 (155th A.C.S. National Meeting -- Industrial and Engineering Chemistry).
By applying the known procedure under normal conditions, it is found firstly that it is only possible to use a fairly reduced number of monomers which can be polymerized by radicals, and that even in this case, it is essential, for obtaining a tangible quantity of copolymer, to add the monomer which can be subjected to radical polymerizations, to the living polymer obtained in the first stage, before adding the radical initiator, and secondly, that the proportion of monomer which can be polymerized by means of radicals is low in the copolymer which is formed. Thus, it is only possible to form 1 to 2% by weight of polyacetovinyl sequences in a block polyethylene, and a few percent of polymer of the acrylic or methacrylic type in block propylene. Furthermore, according to the prior art, it scarcely seems possible to regulate the length of polyolefinic sequences other than by the polymerization temperature and/or possibly by the composition and the concentration of the catalyst system; the very practical industrial procedure, which would consist in controlling the molecular weight of the polymer during the anionic polymerization by extending or shortening the duration of this latter would be very difficult to apply to the known process, because the molecular weight quickly becomes stationary in the presence of the catalysts which are used.
The present invention provides a method which avoids the aforementioned disadvantages. It makes possible the copolymerization of all the monomers polymerizable by means of radicals and the increase as desired, even considerably if this is necessary, of the proportion of monomer fixed in the copolymer during the radical phase; thus, for example, it makes possible the introduction of 6% or more of vinyl acetate instead of 1 to 2% into a polyethylene, and 40% or more of methyl methacrylate, instead of a fraction of percent or a few percent, into a polyolefine. Moreover, the process according to the invention usually makes it possible easily to regulate the length of the chains formed by anionic catalysis in the copolymer. On the other hand, in one particular embodiment of the invention, a polymer practically free from homopolymers can be obtained.
The invention provides various advantages; in particular, it permits of improving the suitability of dyeing of different polymers by introduction into the chain of sequences capable of chemically fixing the dye; it is in fact possible to introduce sequences including functional groups, for example, amino, carboxy or other groups. By means of the present invention, it becomes possible to establish polymers which are compatible with other dissimilar polymers. The invention also permits of improving the adherence of polymers to various surfaces. Other useful applications have moreover been described in the literature referred to above.
The process according to the invention consists of introducing, into the copolymerization medium, before and/or during the anionic polymerization, an adjuvant which is formed by one or more compounds of elements belonging to the group formed by boron and the metals of Group IIB of the Periodic Table of Mendeleev; when the anionic polymerization has reached the desired degree, one or more monomers to be copolymerized are added, without deactivating the coordinated anionic catalyst and in any order, with the first polymer and an appropriate radical catalyst, and the polymerization is continued in known manner.
The adjuvant according to the invention can be represented by the formula M(Y).sub.n, in which M represents a metal belonging to Group IIB of the Periodic Table of Mendeleev, or boron; n is the valency of the element M, and Y represents one or more monovalent hydrocarbon radicals, a hydrogen and/or a halogen atom, particularly chlorine.
According to one particular procedure used by the new process, the adjuvant, introduced into the copolymerization medium in the stage of carrying out the anionic polymerization, is formed by one or more organic compounds of theh aforementioned elements, these being compounds in which the element is only bonded to hydrocarbon radicals. Particularly suitable for this purpose are the derivatives of zinc and cadmium of formula M.sub.Rb.sup.Ra, in which M indicates Zn or Cd, while Ra and Rb, like or different, represent alkyl, aryl, aralkyl, alkaryl or cycloalkyl groups having up to 12 carbon atoms; by way of example, it is possible to mention diethyl zinc, diethyl cadmium, dipropyl zinc, dibutyl zinc, diphenyl zinc, etc., these examples being in no way limitative. Compounds such as zinc, cadmium or boron halides, particularly ZnCl.sub.2, can also be employed.
Each of the two operational phases which constitute the process according to the invention can be effected at a temperature from -78.degree.C to 100.degree.C and preferably between 0.degree. and 80.degree.C; the temperature during the second polymerization, i.e., the radical phase, can according to circumstances be the same as or different from that of the first anionic polymerization.
The coordinated anionic catalysts employed in the first operational phase are organometallic compounds of metals of the Groups IA, IIA and/or IIIA of the periodic table of Mendeleev, accompanied by compounds of one or more transition metals of the Groups IV to VIII of the said Table. Thus, the operating procedure which is particularly practical according to the invention is that in which the anionic catalyst comprises an organic derivative, or optionally a hydride of Li, Mg, Be and/or Al with a Ti or V compound, and in which the adjuvant defined above is preferably an organo-zinc or an organo-cadmium compound.
Although this adjuvant can be introduced into the medium of the first polymerization from the start, it is preferable to add it progressively during this polymerization. It is in fact advantageous to have a certain substantially constant concentration of the said adjuvant throughout the anionic polymerization.
The proportion of this adjuvant to be employed depends inter alia on the percentage of the second monomer which it is desired to obtain in the copolymer. It is usually of the order of 0.01 to 100 moles, and preferably 0.1 to 50 moles, per mole of transition metal compound. Consequently, in the particularly practical case in which the said adjuvant is an R'.sub.2 Zn or R'.sub.2 Cd (R' = alkyl), the content of Zn or Cd is generally from 0.01 to 100 and better still from 0.1 to 50 atoms per atom of transition metal.
As regards the proportions of organometallic catalyst and of transition metal, these proportions are those according to the prior art.
Moreover, as regards the other factors of the anionic phase of the polymerization, namely, the nature and proportion of solvent, the temperature, pressure and nature of the monomer or monomers, they are similar to those of the prior art, as described by way of example in the patents or in the works of Professor Karl Ziegler.
The second phase of the polymerization, in the presence of a catalyst which generates free radicals, is also conducted in the manner known per se. As catalysts, it is possible to use oxygen, hydroperoxides such as for example cumene hydroperoxide, paramenthane hydroperoxide, etc., peroxides such as benzoyl peroxide, lauroyl peroxide, etc., persalts such as potassium persulphate, etc., peracids, etc. In certain cases, the radical catalyst system could be formed by a combination of organo-zinc or organo-cadmium compounds with quinones, such as benzoquinone, naphthoquinone, etc., or phenols.
Among the main monomers for the polymerization or anionic copolymerization are to be considered the olefins or diolefines, such as ethylene, propylene, butene, 4-methylpent-1-ene, butadiene, isoprene, etc., which are mentioned without any limitation. It is possible to copolymerize them according to the invention with polymerizable monomers by means of radicals, such as the vinyl, vinylidene, acryl, methacryl or other monomers, taken individually or in mixtures, particularly vinyl acetate, vinyl chloride, vinylidene chloride; alkyl acrylates or methacrylates; acrylates or methacrylates of R.sup.1 R.sup.2 --N--R-- where R.sup.1 is hydrogen or a lower alkyl, R.sup.2 is a lower alkyl (C.sub.1 to C.sub.4), R being an alkylene having 1 to 6 carbon atoms, sodium or zinc acrylates or methacrylates, etc., acrylonitrile or methacrylonitrile; styrene or its derivatives; vinylcarbazole, vinylpyridines, vinylpyrrolidones; vinyl ethers or thioethers, vinylsilanes; and monoexpoxidised dienes, such as butadiene monoepoxide or the like.
One particular embodiment of the invention which is very advantageous consists in separating the first (anionic) polymer from the medium from which it is obtained before bringing it into contact with the second monomer for the purpose of the radical copolymerization. This separation can be effected by the suspension of the said polymer in the solvent in which the anionic polymerization has taken place being filtered or centrifuged; the solvent keeping in solution the soluble fraction of the products present in the anionic polymerization medium and inter alia metallic compounds and soluble polymers of relatively low molecular weight, is thus eliminated.
The solid polymer which remains is preferably washed with the same or a different solvent, but no operation for deactivating the catalyst is carried out.
For achieving the second operational phase, it is then possible for the polymer as thus prepared to be once again brought into suspension in fresh inert liquid or even in the second monomer itself, after which the dispersion obtained has an appropriate radical catalyst added thereto. By inert liquid, is understood any liquid which does not deactivate the first polymer and does not act chemically either with the latter or with the second monomer or monomers; this liquid can thus be such as a hydrocarbon, for example, hexane, heptane, cyclohexane, benzene, etc., or a halogenated hydrocarbon, such as chlorobenzene, and particularly the same liquid which served as solvent during the first polymerization phase.
By dispersing the first polymer directly in the second monomer, it is possible by adding a radical catalyst to effect a mass copolymerization which leads to products different from those when working in solution. This procedure permits copolymers to be prepared which have very stong contents of groups of the second type, that is to say, originating from the radical catalyst.
It is interesting to note that the embodiment of the invention comprising the separation of the first polymer before the radical polymerization stage makes it possible to obtain a copolymer containing practically no homopolymers.